1. Field of the Invention
The present invention relates generally to electronic devices equipped with an interface such as a Universal Serial Bus (USB), and more particularly to improvements in the power supply to such electronic devices.
2. Description of the Related Art
Various electronic devices having a USB port are known heretofore. These devices are widely used as a mouse, a keyboard, a CD-ROM (Compact Disk Read-only Memory) drive, a CD-R/RW (Compact Disk Recordable/Rewritable) drive, a MO (Magneto-optic) drive and a DVD (Digital Versatile Disk) drive.
The USB interface enables not only data communication between a host machine and a peripheral device but also the supply of electric power from the host machine to the peripheral device. This interface defines lower-power devices with maximum current consumption of 100 mA and high-power devices with maximum current consumption of 500 mA.
Due to such limited maximum current value (500 mA) of the USB interface, devices consuming more power than is admitted (i.e., devices requiring more current than 500 mA) through a single USB port need installation of an extra power supply such as an AC power supply adapter or a battery, which will require an additional power supply circuit and accessories.
However, as the device performance has been significantly improved in recent years, the demand for a space-spacing and cost-reducing device has increased greatly. Especially, there is a keen demand for a device which can operate with current consumption greater than 500 mA so as to realize various functions without using a separate AC power supply adapter or special accessories.